Operation control device for three-joint excavator

ABSTRACT

A speed command value X1 for a first arm 3 is decided depending on a lever input amount in the direction c, d. Assuming that the side d corresponding to move-up of the first arm is positive, the side c corresponding to move-down thereof is negative, and a speed command value resulted upon full lever operation and corresponding to a rated speed of the first arm is 1, X1 is given by -1&lt;X1&lt;1. A speed command value X3 for a third arm 5 is decided depending on a lever input amount in the direction e, f. Assuming that the side f corresponding to dumping of the third arm is positive, the side e corresponding to crowding thereof is negative, and a speed command value resulted upon full lever operation and corresponding to a rated speed of the third arm is 1, X3 is given by -1&lt;X3&lt;1. A speed command value X2 for a second arm 4 is here given by X2=K1×X1+K3×X3 on condition that the side corresponding to move-up of the second arm is positive. With such an operation control system for a 3-articulation type excavator, the excavator can be operated by operators having an ordinary skill continuously over a wide working area specific to 3-articulation type excavators with the same operating feeling as obtained with conventional 2-articulation type excavators.

TECHNICAL FIELD

The present invention relates to an operation control system for anexcavator of the 3-articulation type, i.e., having three articulationsand arms except for a digging bucket, and more particularly to anoperation control system which can utilize advantages of a3-articulation type excavator by using the same operating means as usedin a conventional 2-articulation type excavator.

BACKGROUND ART

The structure of a conventional ordinary excavator is shown in FIG. 14.A working front device 100 is made up of two members, i.e., a boom 101and an arm 102. A bucket 103 for use in excavation work is provided at atip end of the working front device 100. Such an excavator is called the2-articulation type because the bucket 103 serving as a main member tocarry out the work is positioned by two rotatable structural elements,i.e., the boom 101 and the arm 102.

Meanwhile, the so-called two-piece boom type excavator has been employedrecently. One example of the two-piece boom type excavator is shown inFIG. 15. The two-piece boom type excavator is modified from the ordinaryexcavator, shown in FIG. 14, in that a boom 101 of a working frontdevice 100A is divided into two parts, i.e., a first boom 104 and asecond boom 105. Such a two-piece boom type excavator is called here a3-articulation type excavator based on the number of articulations whichtake part in positioning a bucket 103.

The 3-articulation type excavator has an advantage of enabling the workto be easily carried out near an undercarriage of the excavator, whichhas been difficult for the 2-articulation type excavator. Morespecifically, although the 2-articulation type excavator can also beoperated to take a posture shown in FIG. 14 for bringing the bucket 103to a position near the undercarriage, the excavation work cannot beperformed with the arm 102 positioned so horizontally as illustrated. Onthe other hand, in the 3-articulation type excavator, the bucket 103 canbe brought to a position near the undercarriage with the arm 102 heldsubstantially vertical as shown in FIG. 15, allowing the excavation workto be carried out near the undercarriage. Further, the excavation workin a position away from the undercarriage can be performed up to afarther position than reachable with the 2-articulation type excavatorby extending the first boom 104 and the second boom 105 to lie almoststraight.

Another advantage of the 3-articulation type excavator is in enablingthe excavator to turn with a reduced radius of turn. When the directionof the working front device 100A is changed by turning an upper turningstructure 106 for loading dug earth and sand on a dump car or the like,it is difficult for the 2-articulation type excavator to reduce theradius necessary for the turn because the boom 101 has a large overalllength. In the 3-articulation type excavator, the radius necessary forthe turn can be reduced by raising the first boom 104 to take asubstantially vertical posture and making the second boom 105 extendsubstantially horizontally. This means that the 3-articulation typeexcavator is more advantageous in carrying out the work in anarrow-space site.

Next, the conventional operating method will be explained. FIG. 16 showsone example of control levers for use in an ordinary 2-articulation typeexcavator. In normal excavation work, four kinds of operations effectedby the boom, the arm, the bucket and the turn are carried out frequentlyin a combined manner. These four kinds of operations are allocated totwo control levers 107, 108 such that each control lever instructs thetwo kinds of operations. The excavation work is performed by an operatormanipulating the respective levers with the left and right hands. Asanother control lever, there is a (not-shown) travel lever (usuallyassociated with a pedal as well). The travel lever is used independentlyof the other levers 107, 108 in many cases; hence it is not here takeninto consideration.

FIG. 17 shows one example of control levers for use in a 3-articulationtype excavator. As mentioned above, the 3-articulation type excavatorcan be operated to carry out the work over a wide range from a furtherposition to a position nearer to its undercarriage. To realize this,however, the second boom 105 must also be operated in addition to thefirst boom 104 corresponding to the boom 101 of the 2-articulation typeexcavator. Since the four kinds of operations are already allocated tothe two control levers 107, 108, a seesaw type pedal 109 is newlyprovided to operate the second boom 105. See FIG. 4 of JP, A, 62-33937,for example.

Further, JP, A, 7-180173 proposes a control system for a 3-articulationtype excavator. According to the proposed control system, two controllevers are designed to instruct moving speeds of a bucket tip in the X-and Y-directions, respectively, and a predetermined calculation processis executed based on a resultant speed vector signal of those movingspeeds. As a result, in horizontal drawing work, movement of the buckettip can be controlled continuously over a wide range and the bucket canbe moved along a desired path with high accuracy.

DISCLOSURE OF THE INVENTION

With the operating system for the 3-articulation type excavatorconstructed as explained above, a wider working area can be achieved byproviding three articulations, but there is a difficulty in continuouslyoperating the working front device over such a wider area. In otherwords, since the second boom 105 is operated upon the pedal 109 beingtrod down by the operator's foot, it is difficult to operate the secondboom 105 with such fine adjustment as obtainable when operating thelever by the hand, and the second boom 105 cannot be operated in matchwith the first boom 104, the arm 102 and the bucket 103. Accordingly, ascustomary fashion followed in most cases, the second boom 105 is fixedin an extended state when carrying out the work in a far position, andis fixed in a contracted state when carrying out the work in a positionnear the undercarriage.

Further, with the control system proposed in JP, A, 7-180173, the firstboom, the second boom, the arm and the bucket of the 3-articulation typeexcavator can be operated by the two control levers, but these controllevers are special ones designed to instruct the moving speeds of thebucket tip in the X- and Y-directions, respectively, and an operatingmanner of the control levers is much different from that of the ordinarycontrol levers. Therefore, it is hard for operators, who are alreadyfamiliar with the conventional operating manner, to handle the excavatorthrough the proposed control system.

An object of the present invention is to provide an operation controlsystem for a 3-articulation type excavator which enables operatorshaving an ordinary skill to operate the 3-articulation type excavatorcontinuously over a wide working area specific to 3-articulation typeexcavators with the same operating feeling as obtained with conventional2-articulation type excavators.

(1) To achieve the above object, according to the present invention,there is provided an operation control system for a 3-articulation typeexcavator, the operation control system being installed in a3-articulation type excavator comprising an excavator body, a first armrotatably attached to the excavator body, a second arm rotatablyattached to the first arm, a third arm rotatably attached to the secondarm, a digging bucket rotatably attached to the third arm, and ahydraulic drive circuit including a first arm cylinder for driving thefirst arm, a second arm cylinder for driving the second arm, a third armcylinder for driving the third arm, and a bucket cylinder for drivingthe digging bucket, the operation control system comprising first armoperating means including a first control lever for commanding a speedof the first arm depending on operation of the first control lever, andthird arm operating means including a second control lever forcommanding a speed of the third arm depending on operation of the secondcontrol lever, the first arm cylinder and the third arm cylinder of thehydraulic drive circuit being driven in accordance with respectiveoperation signals from the first arm operating means and the third armoperating means, wherein the operation control system further comprisessecond arm commanding means for producing a speed command value for thesecond arm that is calculated from a first value resulted by multiplyinga speed command value indicated by the operation signal from the firstarm operating means by a first arm assistive gain and a second valueresulted by multiplying a speed command value indicated by the operationsignal from the third arm operating means by a third arm assistive gain,and output means for converting the speed command value for the secondarm into a signal, the second arm cylinder of the hydraulic drivecircuit being driven in accordance with the signal from the outputmeans.

While the related art has been described above in connection with, byway of example, the two-piece boom type excavator having a boom dividedinto two members, a 3-articulation type excavator having an arm dividedinto two members also has the same functions as the two-piece boom typeexcavator. Therefore, three members rotatable at their articulations arecalled a first arm, a second arm and a third arm in this Description forthe purpose of more general explanation.

The present invention intends to, as stated above, propose an operationcontrol system for a 3-articulation type excavator which enablesoperators having an ordinary skill to operate the 3-articulation typeexcavator continuously over a wide working area specific to3-articulation type excavators. To realize this, according to thepresent invention, the 3-articulation type excavator is constructed sothat three articulations can be operated by only the same two controllevers as used in 2-articulation type excavators.

Specifically, in a 3-articulation type excavator, the operation ofmoving up a second arm has a substantially equivalent effect to theoperation of moving up a first arm with regard to the direction ofmovement of a bucket, and the operation of moving down the second armhas a substantially equivalent effect to the operation of moving downthe first arm with regard to the direction of movement of the bucket.Likewise, the operation of moving up the second arm has a substantiallyequivalent effect to the operation of dumping (pushing out) a third armwith regard to the direction of movement of the bucket, and theoperation of moving down the second arm has a substantially equivalenteffect to the operation of crowding (pulling in) the third arm withregard to the direction of movement of a bucket.

The present invention has been made in view of the above point, and the3-articulation type excavator of the present invention includes controllevers (first and second control levers) for only the first arm and thethird arm as with conventional 2-articulation type excavators. Thesecond arm is regarded as working to assist the first and third arms,and an input amount for operating the second arm is given by a valuecalculated based on respective values resulted from multiplying inputamounts for operating the first and third arms by respective gainsrepresentative of how extent the first and third arms are to be assistedin their operation, for example, the sum of those values.

By so constructing, the bucket can be operated substantially in a likemanner as that of a 2-articulation type excavator just by operating thetwo control levers as with the 2-articulation type excavator, and thesecond arm is extended and contracted to assist the bucket moving in thedirection intended by an operator. Accordingly, the 3-articulation typeexcavator can be operated continuously over a wide working area specificto 3-articulation type excavators with the same operating feeling asobtained with conventional 2-articulation type excavators.

(2) In the above (1), preferably, the second arm commanding meansincludes adding means for determining, as a calculated value giving thespeed command value for the second arm, the sum of the first value andthe second value.

(3) Also in the above (1), preferably, the second arm commanding meansincludes selecting means for determining, as a calculated value givingthe speed command value for the second arm, a maximum value betweenabsolute values of the first value and the second value.

(4) In the above (1), preferably, the operation control system furthercomprises means for detecting a rotational angle of the first armrelative to the plane on which the excavator body rests, and the secondarm commanding means receives a signal from the detecting means andreduces the third arm assistive gain when the first arm comes close to avertical position relative to the plane on which the excavator bodyrests.

When the first arm comes close to the vertical position, the second armacts to operate the bucket vertically contrary to back-and-forthmovement of the bucket that is intended by the operator when operatingthe third arm. In the present invention, therefore, when the first armcomes close to the vertical position, the third arm assistive gain isreduced to make the second arm less moved upon the operation of thethird arm. This keeps the operator from feeling awkward.

(5) In the above (1), preferably, the operation control system furthercomprises means for detecting a rotational angle of the first armrelative to the plane on which the excavator body rests, and the secondarm commanding means receives a signal from the detecting means andreduces the first arm assistive gain when the first arm comes close to ahorizontal position relative to the plane on which the excavator bodyrests.

When the first arm comes close to the horizontal position, the secondarm acts to operate the bucket back-and-forth contrary to verticalmovement of the bucket that is intended by the operator when operatingthe first arm. In the present invention, therefore, when the first armcomes close to the horizontal position, the first arm assistive gain isreduced to make the second arm less moved upon the operation of thefirst arm. This keeps the operator from feeling awkward.

(6) Further in the above (1), preferably, the operation control systemfurther comprises means for detecting a rotational angle of the secondarm relative to the plane on which the excavator body rests, and thesecond arm commanding means receives a signal from the detecting meansand reduces the third arm assistive gain when the second arm comes closeto a horizontal position relative to the plane on which the excavatorbody rests.

When the second arm comes close to the horizontal position, the secondarm acts to operate the bucket vertically contrary to back-and-forthmovement of the bucket that is intended by the operator when operatingthe third arm. In the present invention, therefore, when the second armcomes close to the horizontal position, the third arm assistive gain isreduced to make the second arm less moved upon the operation of thethird arm. This keeps the operator from feeling awkward.

(7) In the above (1), preferably, the operation control system furthercomprises means for detecting a stroke of the first arm cylinder, andthe second arm commanding means receives a signal from the detectingmeans and increases the first arm assistive gain when the first armcylinder reaches or comes close to the stroke end thereof. In thepresent invention thus constructed, when the first arm cylinder reachesor comes close to the stroke end thereof, the second arm is sped up toprevent the bucket from being quickly slowed down at the stroke end ofthe first arm cylinder. As a result, the operator can be kept fromfeeling awkward.

(8) In the above (1), preferably, the operation control system furthercomprises means for detecting a stroke of the third arm cylinder, andthe second arm commanding means receives a signal from the detectingmeans and increases the third arm assistive gain when the third armcylinder reaches or comes close to the stroke end thereof.

In the present invention thus constructed, when the third arm cylinderreaches or comes close to the stroke end thereof, the second arm is spedup to prevent the bucket from being quickly slowed down at the strokeend of the third arm cylinder. As a result, the operator can be keptfrom feeling awkward.

(9) In the above (1), where the hydraulic drive circuit includes a firstflow control valve, a second flow control valve and a third flow controlvalve for controlling respective flow rates of a hydraulic fluidsupplied to the first arm cylinder, the second arm cylinder and thethird arm cylinder, preferably, the operation control system furthercomprises a pilot circuit for introducing respective pilot pressures tothe first, second and third flow control valves for operation thereof,the pilot circuit including a pair of pilot lines for introducing thepilot pressures to the second flow control valve for operation thereof,and a pair of proportional pressure reducing valves disposed in the pairof pilot lines and operated by output signals from the output means,respectively.

By thus providing proportional pressure reducing valves in pilot linesand operating the proportional pressure reducing valves, the second armcylinder can be easily driven by signals from the output means.

(10) In the above (1), where the first arm operating means and the thirdarm operating means are of the electric lever type outputting electricalsignals as the operation signals, preferably, the second arm commandingmeans receives the electrical signals from the first arm operating meansand the third arm operating means, and determines the speed commandvalues from the received electrical signals.

(11) In the above (1), where the first arm operating means and the thirdarm operating means are of the hydraulic pilot type outputting pilotpressures as the operation signals, preferably, the operation controlsystem further comprises means for detecting the respective pilotpressures from the first arm operating means and the third arm operatingmeans, and the second arm commanding means receives signals from thedetecting means and determines the speed command values from thereceived signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining the structure of a 3-articulation typeexcavator to which the present invention is applied.

FIG. 2 is a diagram showing the configuration of an operation controlsystem for a 3-articulation type excavator according to one embodimentof the present invention, along with a hydraulic circuit.

FIG. 3 is an illustration for explaining an operating manner of controllever units of the operation control system for the 3-articulation typeexcavator according to one embodiment of the present invention.

FIG. 4 is a block diagram showing functions of a controller of theoperation control system for the 3-articulation type excavator accordingto one embodiment of the present invention.

FIG. 5 is a block diagram similar to FIG. 4, showing another embodimentof the present invention for varying an assistive gain.

FIG. 6 is a block diagram similar to FIG. 4, showing still anotherembodiment of the present invention for varying the assistive gain.

FIG. 7 is a block diagram similar to FIG. 4, showing still anotherembodiment of the present invention for varying the assistive gain.

FIG. 8 is a block diagram similar to FIG. 4, showing still anotherembodiment of the present invention for varying the assistive gain.

FIG. 9 is a block diagram similar to FIG. 4, showing another embodimentof the present invention using a maximum value selector instead of anadder.

FIG. 10 is a block diagram showing details of the maximum value selectorshown in FIG. 9.

FIG. 11 is a diagram similar to FIG. 2, showing an embodiment in whichthe present invention is applied to an excavator having control leverunits of the hydraulic pilot type.

FIG. 12 is a block diagram similar to FIG. 4, showing functions of acontroller shown in FIG. 11.

FIG. 13 is a block diagram showing an embodiment in which a differentialpressure gauge is used instead of a pressure gauge.

FIG. 14 is a view for explaining the structure of a conventional2-articulation type excavator.

FIG. 15 is a view for explaining the structure of a two-piece boom typeexcavator as one example of conventional 3-articulation type excavators.

FIG. 16 is an illustration for explaining an operating system of theconventional 2-articulation type excavator.

FIG. 17 is an illustration for explaining an operating manner of controllever units of the conventional two-piece boom type excavator.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described hereunder withreference to the drawings.

To begin with, a first embodiment of the present invention will bedescribed with reference to FIGS. 1 to 4.

In FIG. 1, a working front device 2 of an excavator 1 is of the3-articulation type comprising a first arm 3, a second arm 4 and a thirdarm 5 which are each attached in a vertically rotatable manner. Theworking front device 2 has a base end supported by an excavator body 13(upper turning structure), and a distal end to which a digging bucket 6is attached in a vertically rotatable manner. The first, second andthird arms 3, 4, 5 are driven respectively by first, second and thirdarm cylinders 7, 8, 9, and the bucket 6 is driven by the bucket cylinder10.

FIG. 2 shows one example of a hydraulic circuit. In FIG. 2, denoted by60 is a hydraulic drive circuit including a first arm cylinder 7, asecond arm cylinder 8, a third arm cylinder 9 and a bucket cylinder 10.A working fluid delivered from a hydraulic pump 20 is supplied to thefirst arm cylinder 7, the second arm cylinder 8, the third arm cylinder9 and the bucket cylinder 10 through flow control valves 21, 22, 23, 24,respectively. In addition, there are a turn hydraulic motor and a trackhydraulic motor, not shown, which are similarly connected to thehydraulic pump 20. Although the following description will be made ofthe first arm cylinder 7, the other cylinders also operate in a likemanner.

Further, denoted by 61 is a pilot circuit for introducing pilotpressures to the flow control valves 21, 22, 23, 24 for operationthereof. The pilot circuit 61 comprises a pilot hydraulic source 62, apair of pilot lines 63a, 63b associated with the flow control valve 21and pairs of similar pilot lines 64a, 64b; 65a, 65b, 66a, 66b (only partof which is shown) associated with the flow control valves 22, 23, 24,and proportional pressure reducing valves 29, 30 disposed respectivelyin pilot lines 63, 63 and proportional pressure reducing valves (notshown) disposed in pilot lines 64a, 64b; 65a, 65b; 66a, 66b.

In an operative state, the flow control valve 21 is held in a neutralposition by being supported by springs 27, 28 and its ports is keptblocked; hence the first arm cylinder 7 is not operated. Pilot pressuresadjusted by the proportional pressure reducing valves 29, 30 areintroduced to pilot pressure chambers 25, 26 of the flow control valve21, respectively. When the pilot pressure is established in any of thepilot pressure chambers 25, 26, a valve body of the flow control valve21 is shifted to a position where a force imposed by the establishedpilot pressure is balanced by resilient forces of the springs 27, 28.The working fluid is supplied to the first arm cylinder 7 at a flow ratedepending on the amount of shift of the valve body, causing the firstarm cylinder 7 to extend and contract. The above explanation is equallyapplied to the flow control valves 22, 23, 24.

The proportional pressure reducing valves 29, 30 and the other not-shownproportional pressure reducing valves are adjusted by respective signalsfrom a controller 31 which in turn receives operation signals fromcontrol lever units 11, 12. The control lever units 11, 12 are each ofthe electric lever type outputting an electrical signal as the operationsignal. When control levers 11a, 12a of the control lever units 11, 12are operated, the first arm cylinder 7, the second arm cylinder 8, thethird arm cylinder 9 and the bucket cylinder 10 can be driven at anydesired speeds depending on input amounts by which the control levers11a, 12a are operated.

FIG. 3 shows details of an operating manner of the control lever units11, 12.

In FIG. 3, the operation for the bucket and the turn is exactly the sameas in the conventional excavator. More specifically, when the controllever 11a of the control lever unit 11 disposed on the right side isoperated to the right (a), the bucket 6 is moved to the dumping side(unfolding side) at a speed depending on the input amount. Likewise,when the control lever 11a is operated to the left (b), the bucket 6 ismoved to the crowding side (scooping side) at a speed depending on theinput amount. The upper turning structure constituting the excavatorbody 13 is turned to the right or left at a speed depending on the inputamount by operating the control lever 12a of the control lever unit 12,which is disposed on the left side, to the front (g) or rear (h).

Conventionally, when the control lever 11a of the control lever unit 11is operated in the forward or rearward direction (c, d), only the firstarm 3 is moved. In the present invention, when the control lever 11a ofthe control lever unit 11 is so operated, not only the first arm 3 ismoved down or up at a speed depending on the input amount, but also thesecond arm 4 is moved at a speed depending on a value resulted frommultiplying the input amount by a first arm assistive gain K1.

Further, conventionally, when the control lever 12a of the control leverunit 12 is operated in the leftward or rightward direction (f, e), onlythe third arm 5 is moved. In the present invention, when the controllever 12a of the control lever unit 12 is so operated, not only thethird arm 5 is moved to dump or crowd at a speed depending on the inputamount, but also the second arm 4 is moved at a speed depending on avalue resulted from multiplying the input amount by a third armassistive gain K3.

More specifically, a speed command value X1 for the first arm 3 isdetermined depending on the input amount from the control lever 11a inthe direction c, d. Assuming that the side (d) corresponding to move-upof the first arm is positive, the side (c) corresponding to move-down ofthe first arm is negative, and a speed command value which is resultedupon the control lever being fully operated and corresponds to a ratedspeed of the first arm is 1, X1 is given by:

    -1<X1<1

Also, a speed command value X3 for the first arm 5 is determineddepending on the input amount from the control lever 12a in thedirection e, f. Assuming that the side (f) corresponding to dumping ofthe third arm is positive, the side (e) corresponding to crowding of thethird arm is negative, and a speed command value which is resulted uponthe control lever being fully operated and corresponds to a rated speedof the third arm is 1, X3 is given by:

    -1<X3<1

Here, assuming that the side corresponding to move-up of the second armis positive, a speed command value X2 for the second arm 4 is given by:

    X2=K1×X1+K3×X3

FIG. 4 shows the above operation in the form of a block diagramillustrating functions of the controller 31.

In FIG. 4, the operation signal applied from the control lever unit 11for the first arm 3 and the operation signal applied from the controllever unit 12 for the third arm 5 are introduced to speed command valuefunctions 32, 33 provided in the controller 31, and are converted intothe speed command values X1, X3 for the first and third arms,respectively. The speed command value functions 32, 33 mainly serve toprovide dead zones in the vicinity of neutral points and make non-linearthe relationships between the input amounts from the control levers 11a,11b and the speed command values for actuators. Depending on cases, thespeed command value functions 32, 33 may be omitted.

Based on the above-stated concept, the speed command value X2 for thesecond arm is provided as;

    X2=K1×X1+K3×X3

by multipliers 40, 41 and an adder 42 using the speed command values X1,X3 for the first and third arms and the first and third arm assistivegains K1, K3 which are shown respectively in blocks 50, 51 and stored inthe controller 31 beforehand.

Denoted by 34-39 are saturation functions. How the saturation functions34, 35 take part in the operation of the first arm 3 will be describedbelow.

The first arm speed command value X1 is represented in the controller 31by one value which is positive on the move-up side and negative on themove-down side. On the other hand, in the practical hydraulic circuit,it is required to excite the proportional pressure reducing valve 30when the first arm is moved up, and to excite the proportional pressurereducing valve 29 when the first arm is moved down. The saturationfunctions are used to make conversion necessary for so exciting theproportional pressure reducing valves. Specifically, when the first armspeed command value X1 is positive, the saturation function 34 allowsthe command value to be delivered as it is to the proportional pressurereducing valve 30, but the saturation function 35 prevents a signal frombeing delivered to the proportional pressure reducing valve 29 (i.e.,allows only 0 to be delivered).

Also, when the first arm speed command value X1 is negative, thesaturation function 35 allows the command value to be delivered to theproportional pressure reducing valve 29 while making the sign of thecommand value reversed from positive to negative, but keeping themagnitude of the command value the same. At this time, the saturationfunction 34 prevents a signal from being delivered to the proportionalpressure reducing valve 30 (i.e., allows only 0 to be delivered).

The saturation functions 36, 37; 38, 39 operate likewise such thatrespective signals are delivered to proportional pressure reducingvalves 67 or 68; 69 or 70 depending on whether the second and third armspeed command values X2, X3 are positive or negative. The proportionalpressure reducing valves 67 or 68; 69 or 70 are ones disposed in thepilot lines 64a, 64b; 65a, 65b shown in FIG. 2, but not shown themselvesin FIG. 2.

This embodiment thus constructed operates as follows. Let assume thatK1=K2=0.5, for example, is set in the operation explained below.

When the control lever 11a is fully operated in the direction d withintent to move up the first arm 3, the first arm 3 is moved at the ratedspeed in the up-direction because of X1=1, and simultaneously the secondarm 4 is also moved at a speed half the rated speed in the up-directionfor assisting the movement of the first arm 3 because the command valuefor the second arm 4 is given by X2=0.5. When the control lever 11a isfully operated in the direction c with intent to move down the first arm3, the second arm 5 is also moved at a speed half the rated speed in thedown-direction for assisting the first arm which is moved down at therated speed, because of X1=-1 and X2=-0.5.

Next, when the control lever 12a is fully operated in the direction fwith intent to dump the third arm 5, the third arm 5 is moved at therated speed in the dumping direction because of X3=1, and simultaneouslythe second arm 4 is also moved at a speed half the rated speed in theup-direction for assisting the movement of the second arm 4 because thecommand value for the second arm 4 is given by X2=0.5. When the controllever 12a is fully operated in the direction e with intent to crowd thethird arm 5, the second arm 4 is also moved at a speed half the ratedspeed in the down-direction for assisting the third arm 5 which iscrowded at the rated speed, because of X3=-1 and X2=-0.5.

Further, when the control lever 11a is fully operated in the direction dto move up the first arm 3 and at the same time the control lever 12a isfully operated in the direction f to dump the third arm 5, all the armsare moved at the rated speed in the direction of unfolding thearticulations because of X1=1 and X3=1; hence X2=1.

When the control lever 11a is fully operated in the direction d to moveup the first arm 3 and at the same time the control lever 12a is fullyoperated in the direction e to crowd the third arm 5, the second arm 4is not moved because of X1=1 and X3=-1; hence X2=0. The reason is thatbecause the first arm 3 is instructed to move in the direction ofunfolding the articulation whereas the third arm 5 is instructed to movein the direction of folding the articulation, the respective movementsof the second arm 4 tending to assist the movements of the first andthird arms 3, 5 are canceled.

With this embodiment, as explained above, the three articulated members,including the second arm 4, of the 3-articulation type excavator can beoperated by the same two control levers 11a, 12a as used in theconventional 2-articulation type excavator, without making the operatorfeel awkward. In addition, the 3-articulation type excavator can beoperated continuously over a wide working area, which is an advantageousfeature of 3-articulation type excavators, with the same operatingfeeling as obtained with conventional 2-articulation type excavators.

While the above description has been made as setting the assistive gainsK1, K3 to 0.5, the assistive gains can be set to any desired valuesdepending on circumstances of the work and preference of the operator.For example, if the assistive gains are set to larger values, theexcavator can be operated more quickly in the wide working area.Conversely, if the assistive gains are set to smaller values, theexcavator can be operated with a feeling closer to that of conventionalexcavators.

While the above embodiment has been described as setting the first armassistive gain K1 equal to the third arm assistive gain K3, theseassistive gains may have different values from each other depending on asituation in use of the excavator and preference of the operator. Forexample, if it is desired to move the third arm in a manner closer tothat in conventional excavators, the third arm assistive gain K3 may beset to a smaller value. Alternatively, the third arm assistive gain K3may be set to a larger value for the purpose opposite to the above.

Further, the first arm assistive gain K1 and the third arm assistivegain K3 may be set to variable values as explained below.

In the 2-articulation type excavator shown in FIG. 14 which has beengenerally employed in the past, for the reason of the specificstructure, the boom 101 is used in many cases when the operator intendsto move the position of the bucket 103 vertically. Also, the arm 102 isused in many cases when the operator intends to move the position of thebucket 103 back and forth (i.e., in the direction to move toward/awayfrom the body). As a method for making operators, who have been familiarwith such an operating manner, feel less awkward, it is effective tochange the assistive gains K1, K3 depending on the posture of theworking front device.

FIG. 5 shows an embodiment in which the assistive gain K3 is variable. Afirst arm angle sensor 43 (see FIG. 1) comprising a potentiometer isdisposed at a pivotal point between the first arm 3 and the excavatorbody 13, and a signal from the first arm angle sensor 43 is introducedto a controller 31A (see FIG. 2). The third arm assistive gain K3 whichis usually set to about 0.5, for example, is changed with a function 44such that it is gradually reduced as the angle of the first arm 3relative to the plane, on which the excavator body 13 rests, approaches90 degrees. The resulting value is used as a value output from a block51A.

With this embodiment thus constructed, as the first arm 3 comes closerto its vertical position, the second arm 4 is less moved upon theoperation of the third arm 5. This aims to operate the third arm 5 in asimilar manner as when the control lever of the arm 102 of the2-articulation type excavator is operated, i.e., to operate the thirdarm 5 in such a way as reflecting the intent of the operator to move thebucket position back and forth. In other words, when the first arm 3comes close to the vertical position, the second arm 4 acts to move thebucket 6 vertically contrary to the back-and-forth movement of thebucket 6 that is intended by the operator when operating the third arm5. Therefore, the gain K3 is reduced to suppress the movement of thesecond arm 4 assisting to move the bucket 6 vertically, thereby keepingthe operator from feeling awkward.

While in the above description the first arm angle sensor 43 isconstituted by a potentiometer disposed at the pivotal point between thefirst arm 3 and the excavator body 13 to detect the angle of the firstarm, the target angle of the first arm may be calculated from thegeometrical relationship by providing a position sensor to detect thestroke of the first arm cylinder 7.

FIG. 6 shows an embodiment in which the assistive gain K1 is variable.The first arm angle sensor 43 is disposed as with the embodiment of FIG.5, and a signal from the first arm angle sensor 43 is introduced to acontroller 31B (see FIG. 2). The first arm assistive gain K1 which isusually set to about 0.5, for example, is changed with a function 45such that it is gradually reduced as the angle of the first arm 3relative to the plane, on which the excavator body 13 rests, approaches0 degree. The resulting value is used as a value output from a block50A.

With this embodiment thus constructed, as the first arm 3 comes closerto its horizontal position, the second arm 4 is less moved upon theoperation of the first arm 3. This aims to operate the first arm 3 in asimilar manner as when the control lever of the boom 101 of the2-articulation type excavator is operated, i.e., to operate the firstarm 3 in such a way as reflecting the intent of the operator to move thebucket position vertically. In other words, when the first arm 3 comesclose to the horizontal position, the second arm 4 acts to move thebucket 6 back and forth contrary to the vertical movement of the bucket6 that is intended by the operator when operating the first arm 3.Therefore, the gain K1 is reduced to suppress the movement of the secondarm 4 assisting to move the bucket 6 back and forth, thereby keeping theoperator from feeling awkward.

FIG. 7 shows another embodiment in which the assistive gain K3 isvariable. In addition to the first arm angle sensor 43 disposed as withthe embodiment of FIG. 5, an angle sensor 46 comprising a potentiometerand detecting an angle of the second arm 4 relative to the first arm 3is disposed at the pivotal point between the first arm 3 and the secondarm 4 (see FIG. 1). Signals from these angle sensors are introduced to acontroller 31C (see FIG. 2) where a second arm absolute anglecalculating portion 47 calculates an absolute angle of the second arm 4relative to the excavator body 13. The absolute angle of the second armis introduced to a function 45. The third arm assistive gain K3 which isusually set to about 0.5, for example, is changed with the function 45such that it is gradually reduced as the angle of the second arm 4(second arm absolute angle) relative to the plane, on which theexcavator body 13 rests, approaches 0 degree. The resulting value isused as a value output from the block 51A.

With this embodiment thus constructed, as the second arm 4 comes closerto its horizontal position, the second arm 4 is less moved upon theoperation of the third arm 5. This aims to operate the third arm 5 in asimilar manner as when the control lever of the arm 102 of the2-articulation type excavator is operated, i.e., to operate the thirdarm 5 in such a way as reflecting the intent of the operator to move thebucket position back and forth. In other words, when the second arm 4comes close to the horizontal position, the second arm 4 acts to movethe bucket 6 vertically contrary to the back-and-forth movement of thebucket 6 that is intended by the operator when operating the third arm5. Therefore, the gain K3 is reduced to suppress the movement of thesecond arm 4 assisting to move the bucket 6 vertically, thereby keepingthe operator from feeling awkward.

While in the above description the second arm absolute angle isdetermined by calculation means based on the geometrical relationship bydetecting the relative angle between the first arm 3 and the excavatorbody 13 and the relative angle between the second arm and the first arm,the angle of the second arm 4 relative to the ground surface may bedirectly detected by providing a tilt sensor on the second arm 4.

FIG. 8 shows another embodiment in which the assistive gain K1 isvariable. A sensor 48 for detecting a stroke of the first arm cylinder 7is disposed (see FIG. 1), and a signal from the sensor 48 is introducedto a controller 31D (see FIG. 2). The first arm assistive gain K1 whichis usually set to about 0.5, for example, is changed with a function 49such that it is quickly increased as the first arm cylinder 7 comesclose to the stroke end thereof on the longest or shortest side. Theresulting value is used as a value output from the block 50A.

With this embodiment thus constructed, as the first arm cylinder 7 comescloser to the stroke end, the second arm 4 is caused to speed upquickly. When the first arm cylinder 7 reaches the stroke end and isabruptly stopped while the control lever 11a is being operated to movethe first arm 3 at a speed corresponding to the command value X1 and thethird arm 4 is moving at a speed resulted by multiplying the commandvalue X1 by the first arm assistive gain K1, the movement of the bucket6 is slowed down abruptly. The quick speed-up of the second arm 4 aimsto relieve such an abrupt slow-down of the bucket 6 that is not intendedby the operator. In other words, when the first arm cylinder 7 isstopped at the stroke end, the gain K1 is increased to speed up thesecond arm 4 assisting, thereby preventing the bucket 6 from beingslowed down abruptly and hence keeping the operator from feelingawkward.

While in the above description the sensor 48 for detecting a stroke ofthe first arm cylinder 7 has been assumed to be a sensor for detectingthe cylinder length, the stroke of the first arm cylinder 7 may becalculated based on the geometrical relationship by providing thepotentiometer 43 at the pivotal point between the first arm 3 and theexcavator body 13, as shown in FIG. 1, and detecting the angle of thefirst arm at the current time.

Further, a limit switch for detecting only the stroke end of the firstarm cylinder 7 may be provided to increase the first assistive gain uponthe limit switch being turned on.

Additionally, the above embodiment of FIG. 8 has been explained inconnection with the case where the gain K1 is increased to speed up thesecond arm 4 when the first arm cylinder 7 comes close to or reach thestroke end. As an alternative, the abrupt slow-down of the bucket 6 maybe prevented by a similar sensor 49 for detecting a stroke of the secondarm cylinder 9 (see FIG. 1) and increasing the gain K3 when the thirdarm cylinder 9 comes close to or reach the stroke end, thereby speedingup the second arm 4.

FIGS. 9 and 10 show an embodiment in which the adder 42 is not used tocalculate the command value X2 for the second arm 4 from the valueresulted by multiplying the command value X1 by the assistive gain K1and the value resulted by multiplying the command value X3 by theassistive gain K3.

Outputs of the multipliers 40, 41 are applied to a maximum valueselector 42A. The maximum value selector 42A comprises, as shown in FIG.10, a switch changing-over portion 75, switches 76, 77, and an adder 78.The switch changing-over portion 75 is made up of absolute valuecalculators 75a, 75b, a subtractor 75c, and changing-over signalcalculators 75d, 75e. Values K1X1, K3X3 calculated by the multipliers40, 41 are introduced respectively to the calculators 75a, 75b whichdetermine absolute values of |K1X1| and |K3X3|. The subtractor 75ccalculates ΔKX=|K1K1|-|K3X3|. When ΔKX is 0 or positive, an ON-signal isapplied from the calculator 75d to the switch 76, and when ΔKX isnegative, an ON-signal is applied from the calculator 75e to the switch77. As a result, in the case of |K1X1|≧|K3X3|, the speed command valueX2 for the second arm is provided by X2=K1X1 through the switch 76 andthe adder 78, and in the case of |K1X1|<|K3X3|, the speed command valueX2 for the second arm is provided by X2=K3X3 through the switch 77 andthe adder 78.

By thus determining a maximum value of |K1X1| and |K3X3| as the speedcommand value for the second arm, the working front device can be movedsubstantially in the same manner as obtained when calculating the sum ofK1X1 and K3X3, resulting in similar advantages to those in the firstembodiment.

FIGS. 11 and 12 show an embodiment in which the present invention isapplied to an excavator having control lever units of the hydraulicpilot type. In these drawings, equivalent members or functions to thoseshown in FIGS. 2 to 4 are denoted by the same reference numerals.

In FIG. 11, denoted by 11A, 11B are control lever units of the hydraulicpilot type outputting pilot pressures Pd, Pd; Pf, Pe. The pilotpressures Pc, Pc; Pf, Pe output from the control lever units 11A, 11Bare introduced to pilot pressure chambers 25, 26 of flow control valves21, 23 through pilot lines 63a or 63b; 65a or 65b, respectively, therebyshifting the flow control valves 21, 23. Similar control lever units(not shown) of the hydraulic pilot type are disposed in pilot lines 66a,66b associated with a flow control valve 24. Such proportional pressurereducing valves as used in the first embodiment are not disposed in thepilot lines 63a, 63b; 65a, 65b, and proportional pressure reducingvalves 67, 68 are disposed only in the pilot lines 64a, 64b for thesecond arm 4.

The control lever units 11A, 11B are operated in the same manner as inthe first embodiment shown in FIG. 3. When a control lever 11a isoperated in the direction c, the first arm is moved down and the secondarm is also moved down, while when it is operated in the direction d,the first arm is moved up and the second arm is also moved up. When acontrol lever 12a is operated in the direction f, the third arm isdumped and the second arm is moved up, while when it is operated in thedirection e, the third arm is crowded and the second arm is moved down.

Pressure sensors 80, 81, 82, 83 are connected to the pilot lines 63a,63b; 65a, 65b, respectively, and detection signals from these pressuresensors are input to a controller 31E.

Processing functions of the controller 31E are shown in FIG. 12. Thedetection signals from the pressure sensors 80, 81; 82, 83 areintroduced respectively to multipliers 40, 41 through subtractors 84,85. The subtractors 84, 85 serve to calculate, from the detectionsignals of the pressure sensors 80, 81; 82, 83, command values which areequivalent to the first arm speed command value X1 and the third armspeed command value X3 in the first embodiment. More specifically, thepilot pressure Pc on the first arm down-side (c) detected by thepressure sensor 80 is taken in as a negative value by the subtractor 84,and the pilot pressure Pd on the first arm up-side (d) detected by thepressure sensor 81 is taken in as a positive value by the subtractor 84,thereby providing the speed command value X1 on condition that themove-up direction of the first arm is positive and the move-downdirection thereof is negative. Also, the pilot pressure Pf on the thirdarm dumping-side (f) detected by the pressure sensor 82 is taken in as apositive value by the subtractor 85, and the pilot pressure Pe on thethird arm crowding-side (e) detected by the pressure sensor 83 is takenin as a negative value by the subtractor 85, thereby providing the speedcommand value X3 on condition that the dumping direction of the thirdarm is positive and the crowding direction thereof is negative.

Instead of the pressure sensors 80, 81; 82, 83, differential pressuresensors 86, 87 shown in FIG. 13 may be may be used. In this case,detection signals of the differential pressure sensors 86, 87 can bedirectly used as the first arm speed command value X1 and the third armspeed command value X3, respectively.

The process subsequent to the multipliers 40, 41 is the same as in thefirst embodiment shown in FIG. 4. More specifically, the speed commandvalue X2 for the second arm is provided as;

    X2=K1×X1+K3×X3

by the multipliers 40, 41 and an adder 42 using the speed command valuesX1, X3 for the first and third arms and the first and third armassistive gains K1, K3 which are shown respectively in blocks 50, 51 andstored in the controller 31E beforehand.

When the second arm speed command value X2 is positive, a saturationfunction 36 allows the command value to be delivered as it is to aproportional pressure reducing valve 67, but a saturation function 37prevents a signal from being delivered to a proportional pressurereducing valve 68 (i.e., allows only 0 to be delivered). When the secondarm speed command value X2 is negative, the saturation function 37allows the command value to be delivered to the proportional pressurereducing valve 68 while making the sign of the command value reversedfrom positive to negative, but keeping the magnitude of the commandvalue the same. At this time, the saturation function 36 prevents asignal from being delivered to the proportional pressure reducing valve67 (i.e., allows only 0 to be delivered).

This embodiment thus constructed operates in the same manner as thefirst embodiment except that the flow control valve 21 for the first arm3 and the flow control valve 23 for the third arm 5 are directly drivenby the pilot pressures output from the control lever units 11A, 12A ofthe hydraulic pilot type. With this embodiment, therefore, it is alsopossible to operate the three articulated members, including the secondarm 4, of the 3-articulation type excavator by the same two controllevers 11a, 12a as used in the conventional 2-articulation typeexcavator, without making the operator feel awkward. In addition, the3-articulation type excavator can be operated continuously over a wideworking area, which is an advantageous feature of 3-articulation typeexcavators, with the same operating feeling as obtained withconventional 2-articulation type excavators.

Industrial Applicability

According to the present invention, three articulated members, includinga second arm, of a 3-articulation type excavator can be operated by thesame two control levers as used in a conventional 2-articulation typeexcavator, without making the operator feel awkward. Moreover, the3-articulation type excavator can be operated continuously over a wideworking area, which is an advantageous feature of 3-articulation typeexcavators, with the same operating feeling as obtained withconventional 2-articulation type excavators.

We claim:
 1. An operation control system for a 3-articulation typeexcavator, said operation control system being installed in a3-articulation type excavator (1) comprising an excavator body (13), afirst arm (3) rotatably attached to said excavator body, a second arm(4) rotatably attached to said first arm, a third arm (5) rotatablyattached to said second arm, a digging bucket (6) rotatably attached tosaid third arm, and a hydraulic drive circuit (60) including a first armcylinder (7) for driving said first arm, a second arm cylinder (8) fordriving said second arm, a third arm cylinder (9) for driving said thirdarm, and a bucket cylinder (10) for driving said digging bucket, saidoperation control system comprising first arm operating means (11)including a first control lever (11a) for commanding a speed of saidfirst arm (3) depending on operation of said first control lever (11a),and third arm operating means (12) including a second control lever(12a) for commanding a speed of said third arm (5) depending onoperation of said second control lever (12a), said first arm cylinder(7) and said third arm cylinder (9) of said hydraulic drive circuit (60)being driven in accordance with respective operation signals from saidfirst arm operating means (11) and said third arm operating means (12),wherein:said operation control system further comprises second armcommanding means (32, 33, 40, 41, 42, 50, 51) for producing a speedcommand value (X2) for said second arm (4) that is calculated from afirst value resulted by multiplying a speed command value (X1) indicatedby the operation signal from said first arm operating means (11) by afirst arm assistive gain (K1) and a second value resulted by multiplyinga speed command value (X3) indicated by the operation signal from saidthird arm operating means (12) by a third arm assistive gain (K3), andoutput means (36, 37) for converting the speed command value (X2) forsaid second arm (4) into a signal, said second arm cylinder (8) of saidhydraulic drive circuit (60) being driven in accordance with the signalfrom said output means.
 2. An operation control system for a3-articulation type excavator according to claim 1, wherein said secondarm commanding means (32, 33, 40, 41, 42, 50, 51) includes adding means(42) for determining, as a calculated value giving the speed commandvalue (X2) for said second arm (4), the sum of said first value and saidsecond value.
 3. An operation control system for a 3-articulation typeexcavator according to claim 1, wherein said second arm commanding means(32, 33, 40, 41, 42A, 50, 51) includes selecting means (42A) fordetermining, as a calculated value giving the speed command value (X2)for said second arm (4), a maximum value between absolute values of saidfirst value and said second value.
 4. An operation control system for a3-articulation type excavator according to claim 1, further comprisingmeans (43) for detecting a rotational angle of said first arm (3)relative to the plane on which said excavator body (13) rests, whereinsaid second arm commanding means (32, 33, 40, 41, 42, 44, 50, 51A)receives a signal from said detecting means (43) and reduces the thirdarm assistive gain (K3) when said first arm (3) comes close to avertical position relative to the plane on which said excavator body(13) rests.
 5. An operation control system for a 3-articulation typeexcavator according to claim 1, further comprising means (43) fordetecting a rotational angle of said first arm (3) relative to the planeon which said excavator body (13) rests, wherein said second armcommanding means (32, 33, 40, 41, 42, 45, 50A, 51) receives a signalfrom said detecting means (43) and reduces the first arm assistive gain(K1) when said first arm (3) comes close to a horizontal positionrelative to the plane on which said excavator body (13) rests.
 6. Anoperation control system for a 3-articulation type excavator accordingto claim 1, further comprising means (43, 46, 47) for detecting arotational angle of said second arm (4) relative to the plane on whichsaid excavator body (13) rests, wherein said second arm commanding means(32, 33, 40, 41, 42, 45, 50, 51A) receives a signal from said detectingmeans (43, 46, 47) and reduces the third arm assistive gain (K3) whensaid second arm (4) comes close to a horizontal position relative to theplane on which said excavator body (13) rests.
 7. An operation controlsystem for a 3-articulation type excavator according to claim 1, furthercomprising means (48) for detecting a stroke of said first arm cylinder(7), wherein said second arm commanding means (32, 33, 40, 41, 42, 49,50A, 51) receives a signal from said detecting means (48) and increasesthe first arm assistive gain (K1) when said first arm cylinder (7)reaches or comes close to the stroke end thereof.
 8. An operationcontrol system for a 3-articulation type excavator according to claim 1,further comprising means (49) for detecting a stroke of said third armcylinder (9), wherein said second arm commanding means (32, 33, 40, 41,42, 50, 51) receives a signal from said detecting means (49) andincreases the third arm assistive gain (K3) when said third arm cylinder(9) reaches or comes close to the stroke end thereof.
 9. An operationcontrol system for a 3-articulation type excavator (1) according toclaim 1, wherein said hydraulic drive circuit includes a first flowcontrol valve (21), a second flow control valve (22) and a third flowcontrol valve (23) for controlling respective flow rates of a hydraulicfluid supplied to said first arm cylinder (7), said second arm cylinder(8) and said third arm cylinder (9), and wherein:said operation controlsystem further comprises a pilot circuit (61) for introducing respectivepilot pressures to said first, second and third flow control valves (21,22, 23) for operation thereof, said pilot circuit including a pair ofpilot lines (64a, 64b) for introducing the pilot pressures to saidsecond flow control valve (22) for operation thereof, and a pair ofproportional pressure reducing valves (67, 68) disposed in said pair ofpilot lines and operated by output signals from said output means (36,37), respectively.
 10. An operation control system for a 3-articulationtype excavator (1) according to claim 1, wherein said first armoperating means (11) and said third arm operating means (12) are of theelectric lever type outputting electrical signals as said operationsignals, wherein:said second arm commanding means (32, 33, 40, 41, 42,50, 51) receives the electrical signals from said first arm operatingmeans (11) and said third arm operating means (12), and determines saidspeed command values (X1, X3) from the received electrical signals. 11.An operation control system for a 3-articulation type excavator (1)according to claim 1, wherein said first arm operating means (11A) andsaid third arm operating means (12A) are of the hydraulic pilot typeoutputting pilot pressures as said operation signals, wherein:saidoperation control system further comprises means (80, 81, 82, 83; 86,87) for detecting the respective pilot pressures from said first armoperating means (11A) and said third arm operating means (12A), and saidsecond arm commanding means (40, 41, 42, 50, 51, 84, 85) receivessignals from said detecting means (80, 81, 82, 83; 86, 87) anddetermines said speed command values (X1, X3) from the received signals.